One page, read top to bottom: the endpoint and the request a reader can reproduce at once, the boundary (queries only; every write goes through REST), the query shape with three worked queries, the entity names and arguments it accepts, the home-page query that is the reason to use it, who may call it, what a query costs, and when REST is the better choice.
It is a GraphQL-style endpoint rather than a full GraphQL server, with its own rules about what a query looks like, so read them before pointing a GraphQL client library at it. It uses the same field names and filters as REST, so Shaping the response with properties and Filters, ordering and paging carry over.